I think that was after others took over the UI development. The back end of that program also was still C as far as I remember from their presentation and the move was mostly motivated by the GTK community, the documentation and different priorities on cross platform support.
Did he have an "attitude" about C++ in general? I thought he only commented on it with respect to operating system development. He did make much more general statements about Java, though.
I think I watched an interview with him where he talked about Subsurface project. In that interview he said that C++ is not all that bad but he still prefers C because he's so used to it and will continue write C code forever. I don't remember title of the video though.